Write a Python program to implement a stack using list.

class Stack:
    def __init__(self):
        self.stack = []

    def is_empty(self):
        return self.stack == []

    def push(self, item):
        self.stack.append(item)

    def pop(self):
        return self.stack.pop()

    def size(self):
        return len(self.stack)

s = Stack()
print(s.is_empty())
s.push(4)
s.push('dog')
print(s.pop())
print(s.size())